Cut tofu into large cubes (1inch x 1inch) and place into mixing bowl.
Drizzle oil onto tofu while tossing gently so you don’t mush the tofu until just coated.
Add sesame seeds and crushed black pepper onto tofu and coat by lightly tossing.

Heat a heavy pan (cast iron works well, can be done in wok too) and add oil.
As oil starts to haze, add tofu and sear until tofu is lightly browned. It is KEY to add the tofu to a hot pan and then leave it alone, when the tofu moves off the pan easily, then toss a couple times and leave it alone again so as to lightly brown all sides.

Once tofu is lightly browned, add the mushrooms. Use the same technique as with the tofu – toss a couple times and leave it alone for a bit and repeat.

Then, once mushrooms are browned, add mirin and toss. Be careful as it has alcohol and may flame up.
Before all liquid has evaporated add tamari to taste, go lighter rather than heavier as reducing tamari will increase saltiness.

Place washed spinach into mixing bowl. Add the tofu and mushrooms hot into the spinach as to slightly wilt the spinach. Best if served immediately when the spinach has dual textures of slightly wilted and some uncooked. Serve and enjoy.